1. Field of the Invention
The present invention relates to a developing agent carrier manufacturing method, a developing agent carrier, a developing device and an image forming apparatus, and in particular relates to a developing agent carrier manufacturing method, a developing agent carrier manufactured by the method, a developing device provided with the developing agent carrier and an image forming apparatus provided with the developing device.
2. Description of the Prior Art
Image forming apparatuses such as a printer, a copier and a facsimile, which take advantage of electrophotography, are adapted to form a toner image on a recording medium, e.g. a paper, through a series of image forming processes including an electrifying step, an exposure step, a developing step, a transfer step, a fixing step and the like.
Such image forming apparatuses are provided with a developing device arranged to face a photosensitive body carrying an electrostatic latent image and having a developing roller (developing agent carrier) for carrying toner. The developing device converts the latent image to a toner image and visualizes the same by applying the toner from the developing roller to the photosensitive body in the developing step.
Conventionally known examples of the developing roller employed in such a developing device include a developing roller of the type having an outer peripheral surface roughened into irregularities by blast treatment (see, e.g., JP-A2003-263018). This blast treatment enables the developing roller to carry the toner reliably.
However, since the irregularities are formed by the blast treatment in the developing roller disclosed in the afore-mentioned prior art reference, it is often the case that the irregularities thus formed become uneven in shape, size and distribution, thereby degrading development characteristics.
Taking a specific example, the distribution of the quantity of the toner carried on the outer peripheral surface of the developing roller may be uneven in some cases, and the tumbling capability (ease of tumbling movement) of toner particles on the outer peripheral surface of the developing roller may grow non-uniform in another case. For this reason, it is often the case that defective electrification or poor conveyance of the toner occurs locally at the time when the toner on the developing roller is frictionally electrified by means of a restriction blade. As a consequence, defective development such as a so-called “fog” or the like takes place.
Further, the irregularities formed by the blast treatment have protrusion portions whose tip end is relatively sharp. Therefore, the irregularities are apt to wear out by the contact with the restriction blade or the like, which means that the developing roller of the afore-mentioned prior art reference suffers from reduced durability.
Furthermore, in order to make the conveyance ability of the toner excellent by the irregularities on the outer peripheral surface of the developing roller, it is preferred that a pitch between the depressions or ridges of the irregularities is set to be lower than 100 mm or less.
Moreover, a demand has existed for a method by which the irregularities on an outer peripheral surface of a developing roller can be set into a desired arbitrary shape.
In addition, in general, for the purpose of reducing a weight, a developing roller includes a main body formed from a hollow cylindrical shape member, and flange members having rotation shafts which are rotatably supported by shaft bearing means are respectively fitted or pushed into openings provided on both the ends of the cylindrical shape member in such a developing roller, formation of the irregularities is carried out after the flange members have been fitted into the openings of the cylindrical shape member so that the axes of rotation shafts of the flange members are aligned with each other. However, such a hollow cylindrical shape member as described above is likely to be deformed as compared with a solid cylindrical shape member (rod-like member) due to its reduced rigidity. Further, rigidity differs between the end portions of the cylindrical shape member in which the flange members are respectively fitted and a portion other than the end portions. For these reasons, it was difficult to form the irregularities uniformly on the outer peripheral surface of the developing roller. Furthermore, if the cylindrical shape member is deformed, contacting pressure between the developing roller and the restriction blade changes, thus leading to the case that defective electrification or poor conveyance of the toner occurs.